The invention relates to a manual drive to produce a rotary movement operating in both directions, that is, clockwise and counter-clockwise, and is usable with particular advantage in adjustment systems of vehicle seats. It is characterized by a finely-stepped quiet functioning.
An adjustment drive of the generic type which is to be used in particular as an articulated fitment for seat height or backrest incline adjustment in vehicle seats is described in German Patent Application DE 3 608 858 A1. According to this reference, a shaft connected to a rotary joint is mounted in a frame. The adjustment is made through a cogged setting wheel and an operating arm having two lever-like entrainment members. Two coil springs under their own tension against the cylindrical inner face of the receiving socket. Connected to the receiving socket is a setting wheel which has entrainment teeth and which is associated with the lever-like entrainment member of the operating arm. The oppositely arranged coil springs each adjoin with one end area on one end of a shaft projecting into the receiving socket and with the other end area in both directions, with some play, near a stop connected to the setting wheel. During swivel movements of the operating arm, the coil spring--which locks according the direction of rotation--is blocked by running up the stop so that the swivel movement can be converted into a rotary movement. The two entrainment members are switched through a separate spring and stop so that, depending on the swivel direction of the operating arm, the one or other entrainment member passes into engagement with an entrainment cog of the setting wheel.
With this articulated fitment the distance between each entrainment cog is so great that during switching, a comparatively large angular path has to be traveled to make up the idling process. A finely stepped adjustment of a seat is thus not possible. A further disadvantage of the adjustment drive is that the entrainment member projects over the outer contour of the setting wheel and thus increases the structural space of the adjustment drive, thus requiring the housing for the adjustment drive to be correspondingly large.
Furthermore drives called ratchets are known which have swivel detent elements supporting comparatively fine teething. The teething of the detent elements is held in permanent engagement with the counter teething of the drive through a spring. The disadvantage here however is that the returning idling stroke of the drive leads to noises because the teething of the detent element and drive wheel slide on each other.
U.S. Pat. No. 4,903,931 discloses a manual drive for a vehicle seat wherein a displacement force exerted by a drive lever is transferred through ratchet pawls to a toothed element or a drive axle connected to the toothed element. The ratchet pawls are thereby arranged to swivel in a housing which can swivel about the drive axle. Each ratchet pawl is allocated a spring which brings each ratchet pawl adjacent the toothed element. To ensure that during an upward or downward movement of the drive lever only one ratchet pawl engages with the toothed element, a cam is provided which is connected to a change-over lever which, depending on the position, presses each detent pawl away from the toothed element. To reverse the displacement direction, the change-over lever must be manually switched over.
It is therefore desirable to provide a manual drive acting in both directions to produce a rotary movement which, by using keyed locking elements, allows a very finely stepped adjustment while at the same time avoiding much of the noises normally associated with such adjustment drive, the so-called ratchet noises. Also desirable is to practically eliminate the noticeable idling stroke through the drive lever.
Further, it is desirable to provide a drive including lever-like entrainment members mounted on the operating arm that do not project over the cogged setting wheel in order to achieve a more compact structural shape.